With the development of the information technology, information-recording device, such as hard disk driver (HDD), is widely used. The HDD can store data by means of the magnetic recording medium. FIG. 1 shows the typical configuration of a conventional HDD, in which disk 10 spins about axis 11 at relatively high speed, and drive arm 16 controls the head element (not shown) located at the tip of the HGA 17 to fly above the surface of the disk 10 such that the head element can perform read/write operation at various tracks. Generally, a voice coil motor (VCM) 15 serves as the main actuator to make the drive arm 16 mounted on the carrier 14 rotate about bearing 13, so that the course adjustment of the position of the head element relative to the surface of the disk 10 can be performed.
However, because of the large inertia of the VCM, a quick and fine position control of the head element cannot be obtained. In order to perform fine adjustment to the position of the head element, an HGA 17 is provided on the tip of the drive arm 16. FIG. 2a shows the detail structure of the conventional HGA 17 shown in FIG. 1, which is disclosed in U.S. Pat. No. 6,671,131. FIG. 2b shows the enlarged view of the front end of the HGA 17. As can be seen, the conventional HGA 17 includes a suspension 171 and a micro-actuator 18 mounted in the tongue area of the suspension 171. The head element 19 is mounted within the micro-actuator 18 and can move independent of the suspension 171 by the actuation of the micro-actuator 18. Therefore, the position of the head element 19 can be adjusted at much smaller scale and much higher frequency. Accordingly, the TPI (tracks per inch) value of the HDD can be increased by 50%.
As can be seen in FIGS. 2a and 2b, the conventional micro-actuator 18 with head element 19 is mounted at the suspension tongue (not shown) of the suspension 171. FIG. 2c shows the exploded perspective view of the conventional micro-actuator 18 in turn over state. The micro-actuator 18 includes metal frame composed of bottom portion 186, support portion 182, two opposite arm 184 and 185 extending from the bottom portion 186 and support portion 182 perpendicularly, and two pieces of piezoelectric PZT (Piezoelectric Lead Zirconate Titanate) 181 and 183 are attached to the outside surfaces of two opposite arms. The PZT pieces 181, 183 can be made from ceramics material, or may be thin-film PZT. The head element 19 constituted with slider and the read/writer transducer (not shown) located at the center of the slider is mounted on the support portion 182 of the metal frame. The micro-actuator 18 with the head element 19 is mounted on the HGA 17 by fixedly securing the bottom portion 186 of the micro-actuator to the suspension tongue. Micro-actuator 18 is electrically connected to the suspension pad 172 via suspension traces 173, other end of which is connected to three electrical bonding balls 192 (GBB or SBB) formed on each outside surface of the arms 184 and 185. Similarly, multiple electrical bonding balls for example four electrical bonding balls 191 (GBB or SBB) are located on front surface of the head element 19, by which the head element 19 is connected with the suspension pad 172 via suspension traces 173. Thus, the power supply and control signals can be applied to the micro-actuator 18 and the head element 19 via the suspension traces 173.
As shown in FIG. 2d, when driving signals are applied to the PZT pieces 181 and 183 via traces 173, the PZT pieces 181 and 183 will shrink or expand in response to the driving signals so that the arms 184 and 185 deform together with the PZT pieces. The head element 19 mounted on the support portion of the micro-actuator will displace in a small scale, thus the fine adjustment of the head element will be achieved.
As can be learned from the operation procedure described above, conventional micro-actuator 18 works in a translation mode. In this case, the head element 19 will intermittently sway due to the shrinking and expanding of the PZT pieces 181 and 183, which intermittent sway movement will in turn cause a reaction force F′ applied to the suspension tongue by the bottom portion 186 of the micro-actuator. This intermittent reaction force will lead to the resonance of the suspension 171 such that the performance of the HDD, particularly the servo bandwidth of the HDD is limited.
FIG. 2e is the graph showing the resonance of the PZT and base plate of the suspension respectively according to the prior art, in which the horizontal axis represents resonance frequency (Hz) while the vertical axis represents vibration gain (dB). The curve 121 shows the curve of resonance gain vs. the exciting frequency of PZT pieces and the curve 122 shows the curve of the resonance gain vs. the exciting frequency of the base plate of the suspension. As can be seen from the figure, the curve for the PZT exciting and the resonance curve for the base plate of the suspension are substantially similar, which means that the sway of the PZT pieces will excite the resonance of the base plate of the suspension. This is disadvantageous for the fine position of the head element 19.